Movable core spark plug



B. MILLER MOVABLE GORE SPARK PLUG Filed April l0, 1939 May 2s, 1940.

1am-1m UNITED STAT A amaze MovAnLE conn sami; PLUG Benjamin Miller', Richmond Hill, N. Y., assignor to Power Patents Company, Hillside, N. J., a corporation ot- Maine ApplicationApril 10, 1939, Serial No. 267,026 Y variation indicator.

In the usual spark ignition internal combustion engine, the head of each cylinder is provided with a single threaded aperture or spark plug hole into which the spark plug element of the ignition system fits. The primary object of the present invention is to provide a novel design of movable core spark plug fitting which can function both as a spark plug and as a pressure variation indicator for studying engine cylinder pressure variations such as occurv during the power or combustionphase of a working cycle. In its broader aspects the cylinder pressures.'

.With the above' and other objects and features in view, the invention consists ln the improved spark plug-pressure transmitting and indicaor device whichsis hereinafter described and particularly defined lin the accompanying claims.

In the iollowingydescription of the invention reference 'will be made to the attached drawing.

in which:

cordance with the present invention, p shown in elevation:

invention features a unitary design of sparkvplug-pressure indicating device in which the center electrode of the spark plug and its dielectric core is moveably mounted within the cylindrical spark plug shell for reciprocation as a piston therein in response to pressure variations in the engine cylinder with which the spark gap is operatively associated, together with elastic pressure indicating means for restraining the movement of the piston, and means for delivering high voltage current for projecting the spark to the center electrode without interfering with free movement of the pressure transmitting piston. More specic objects of the invention are to provide a device so disposed as to allow so far as practicable for the use of standard spark plug cores and parts in the assembly; to provide a design permittingeasy replacement oi parts and ready threading of the unit into one engine spark-plug aperture where only a limited accessible space is available; and to provide a design which will insure the maintenance of atmospheric pressurewithin the cylinder in which the'piston reciprocates while ex'' posing the working face of the piston to engine (Cl. 1233-4169)A Fig. 2 is a cross-sectional view taken on the line 2-'2 of Fig. 1; and

Fig. 3 is a cross-sectional view taken on the line 3-3 of Fig. 1.

Referring to Fig. 1, the device therein iilusi. trated embodies a tubular metal cylinder or casing l0 having external threads I2 at the forward end thereof which are adaptedto engage thev .threads of' the spark plug hole in an internal combustion engine cylinder head. 'I'hat end of l casing I0 which carries threads i2 also supports an electrode I4 corresponding to the usual grounded electrode of a spark plug. The casing I0 has been shown as preferably having a small cross-section throughout the greater portion of its length. A smooth cylinder bore i6 of uniform cross-sectional area throughout its length lies within the larger cross-sectional end of the casing I0. An annular shoulder i8 is formed on 20 the inner wall of casing I0 at the forward end of cylinder I6 where the central bore of the casing is reduced in size. At the rearward end 'of the casing and bore IG, thev casing is internally threaded at 20 for a purpose which will be later '25 referred to. 'if

At a point intermediate the ends of the casing i0, a circular aperture 22 is provided in the wall of the casing. Also that portion of the casing adjacent aperture 22 .is externally threaded by 30 threads 24 extending to both sides of the aperture. A second aperture 23 is provided in the wall of casing I0 at the forward end of bore i6I for the purpose of admitting air to the cylinder bore.-

The principal pressure transmitting element of the device is a piston 26 which is movably mounted within bore I6 for reciprocation therein in response to variations in pressure occurring trode end of the device is located when in service. 'The principal pressure transmitting element of the piston- 26 has been' illustrated as aV tubular cylindrical metal shell 28 mounted coaxially within cylinder II and casing Il. Another important 45 element of the piston is a wire electrode 30 which is mounted'centrally andcoaxially within the shell 28 and extends in length from a point adjacent electrode I4 tjoa point approximately in line with the center of aperture 22 in Acasing l0. 50 A great part of the-length of the electrode 30 intermediate its ends is encased within a dielectric spark plug shell' or core $2 preferably constructed or porcelain or other strong high temperature resistant ceramic material. This-dielectric core 55 cross-section at its electrode end, and a larger 15 Y within the engine cylinderwithin which the elec- 4,0

$2 (which is sho partly in elevation and partly in dotted outline) serves as an insulating wall between electrode 3d and the metal shell 223, all of these parts being built into a unitary piston assembly. A turned-over end oi shell 29 which faces the shoulder lil at the electrode end of cylinder bore i6 is nish'ed with a smooth anelectrode end of casing l0. A flexible metal ring gasket 68 is preferably mounted between shoulder i8 andface 34 of the piston for the purpose of preventing leakage of combustion gases from the engine cylinder and space 38 into cylinder it. A ilexible diaphragm connecting the piston and casing lll might be'used in place of gasket t8.

The forward portion of the shell 2d (shown in elevation) and the rearward part of the dielectric core 32 have been .illustrated as shaped in a design similar to that of most sparlr plug elements now on the market.' The space lying between the tapered rear portion d@ of the dielec=` tric core and the metal shell 2t has been shown as occupied by a cylindrical dielectric sleeve et and by a lling 44 preferably of some dielectric cement such as a heat hardenable phenol-form aldehyde resin. Sleeve 42 extends rearwardly lieyond that end of wire 3Il which is in line with aperture 22, and a dielectric plug closure @d is fitted into that end of sleeve d2 in position to surround that portion of the end oi wire t@ which is not encased by the shell 32. .apertures are formed in the walls of each of elements 28 and 42 and in plug 46 in line with aperture 22 in the walls; of casing lll, such apertures in combination forming a socket 48 having a conical bottom into which projects one beveled side of end 50 of electrode 36 (see Fig. 2).

A metal plug 52 is aflixed to the rearward end of piston 26 and shell 28, and a spherical metal ball 54 is preferably fitted into a semispherical socket in that face of plug 52 which forms the rearward end of the piston. An air gap 55 is preferably provided between adjacent sides `ot the metal plug 52 and dielectric plug 46, in or= der to protect the plug 46y and other dielectric parts of the piston against any of the compres sion strains to which the metal parts 28 and 54A are subjected.

To supply the high potential electrical im pulses for projecting sparks across gap 85. a conductor plug through aperture 22 with its end .shaped to fit tightly in socket 48. Electrical impulses for actu-1.

ating the spark may be delivered to plug 56 froml l the distributor of the engine by a lead-wire which has not been illustrated. Plug 86 comprises essentially a center wire 58, one end 6U of which lis beveled to have 'a tight sliding contact with beveled end 50 of electrode 30 at the base of" socket 48, while the other end of wire 58 is af'- fixedto a connector cap 62. The construction of plug 56 is completed by a dielectric shell 6 which encases wire 58 and which has a beveled end shaped to form,` a tight dt within socket dt.

56 has been shown as inserted aeoaaao r in aperture 22 of the casing I0, and is provided with means including a pair of clamping rings t and a pair of ring nuts 66 threaded to` en-s gage the threaded portion 24 of casing I0, whereby plug 56- can be adjustably centered in aperture 22.

This design was developedV to permit easy connection and disconnection of the spark gap with the source of energizing current while providing a connection which wouldnot interfere with initial mounting of the spark plug in a diicultly accessible spark plug aperture. f

With a construction such as described, a. 'continuous sliding metal-to-metal contact can be maintained between the `beveled end- 80 of wire 't8 in socket 48 and the beveled end 50 of electrode 30, to thereby insure satisfactory functioning of thedevice as a spark plug, while the pisn ton 26 is reciprocated within the cylinder I6 in a path which may be only a few millionths of an inch in length at a maximum, in response to variations in pressure in the cylinder into which spark gap 35 extends. It will be understood that that end of plug 56 4which extends into socket 48 has suiiicient lateral flexibility so thatit can reciprocate with the piston 28 without serious interference with the piston movement. The internal threads 20 at the rearward end of the caslll aiord the means for operatively contacting the rearward end of the piston withV an elastic means for indicating pressure variations and*l for restraining movement of the piston.

ln order to allow for the use of a cathode ray oscillograph, or similar device, for obtaining visual records of the variations in cylinder pressure which can be accurately transmitted bythe device forming the subject ofthis invention, a

preferred' elastic pressure indicating and piston restraining means has been shown' in the shape of a piezo-electric generator 10. This generator lll is operatively connected with the pressure v transmitting unit of Fig. 1 in a way such that an electric voltage'is generated thereby which 'varies inh proportion to variations in pressure Plug 56 is shown as dimensioned to nt loosely' which are developed in the cylinder within which gap 35 is mounted. Voltage generator 'I0 is mounted in a tubular metal casing 12 having external threads which are adapted to ,engage the internal threads 20 at the rearward end of 'casing 88; Generator 10 consists essentially of a pair of quartz crystals I4k which are vmounted face to face in casing 12 between a pair of metal .electrodes 'l5-"I6 which are grounded to the shell i8 of thev spark plug. Variations in gas pressure within the cylinder in which gap 35 is located, are transmitted by piston 26 to electrode I5 -and through it to crystals 14 through a metal dlaphragm closure I8 forthat end of casing 'I2 which contacts ball 54 at the rearward end of the piston. Crystals 'I4 are mounted in casing -12 in opposed relation with respect to their electrical axes, and their adjacent faces are separated by, and contact, a third insulated electrode 80. By this arrangement of the crystals, when they are subjected to pressure applied along the longitudinal axis of the casing 12 they both develop charges of the same sign atv electrode 80, and the potential ofthe chargel varies with variations in the pressure applied to the crystals. A lead wire 82 conducts the electric charge thus developed on electrode "to an ampliiier (not shown) which may in turn be hooked up with a cathode ray oscillograph. n

The rearward end of casing 12 has been shown as threaded for engagement by a threaded cap u for the casing. A plunger Il is mounted inside casing 12 and 'attached to cap 84 for movement therewith to apply an initial compression to crystals 14. By advancing casing 12 along threads 20, plate 1l is forced into tight pressure contact with the ball M on piston 26. By this arrangement gasket Il may be subjected Yto a pressure suillcient toseal prior to instituting operation of the spark plug-indicating device.

Having thus described the invention, what is claimed as new is:

1. A combined spark plug-pressure indicating unit comprising an lexternally threaded tubular metal casing having an electrode mounted at the forward end thereof, a smooth wall cylinder bore within the casing, apiston mounted for reciprocation within the cylinder bore in response y to variations in pressure in a chamber with which the forward end of the casing communicates in,

service, said piston comprising an axially disposed wire electrode and a dielectric core embedding the wire electrode, a spark gap formed between the casing electrode and the forward end of the wire electrode, means for supplying current for actuating the spark gap including an aperture in the wall of the casing intermediate its ends, a socket in the piston aligned with said casing aperture and with therearward end of the coaxial wire electrode. and an insulated leadn in wire conductor having an end adapted for insertion into said socketthroug'h said aperture with an uninsulated terminal in sliding contact with the rearward end of said electrode, and elastic means for restraining the movement of the piston.

2. Apparatus as defined in 4claim 1 together with means for clamping the lead-in wire conductor in center position within said lateral casing aperture and piston socket, the end of said lead-in wire being shaped to form a loose fit in said aperture and a tight fit within said socket.

3. A combined spark plug-pressure indicating unit comprising, an externally threaded tubular metal casing having an electrode mounted at the forward end thereof, a smooth Wall cylinder bore within the casing, a piston mounted for reciprocation within the cylinder bore in response to variations in pressure in a chamber with which the forward end of the casing communicates in service, said piston comprising, an axially disposed wire electrode and a dielectric core embedding the wire electrode, a spark gap formed between the casing electrode and the forward end of the wire electrode, means'for supplying current for energizing the spark gap without interference with the movement of the piston, a metal closure for the rearward end of said piston having a spherical ball contact element mounted on the rearward face thereof and elastic means for restraining the movement of the piston.

BENJAMIN MILLER. 

